1. Field of the Invention
The present invention relates generally to a hydraulic braking apparatus for bicycles which is manually actuated to enforce braking conditions, and more particularly to an improved hydraulic braking system characterized by an overall enhanced performance that makes it possible to obtain a highly efficient brake system most suitable to the bicycle.
2. Description of the Prior Art
Many kinds of hydraulic braking systems actuated by a hand operated mechanism are known to be used for braking purposes with conventional bicycles. Hydraulic braking systems typically utilize a master cylinder assembly in fluid communication with slave cylinders, wherein the master cylinder assembly is manually actuated by a brake handle. The manual pressure on the handle is transmitted by the master cylinder assembly via the hydraulic fluid to actuate the slave cylinders, which in turn force brake pads positioned on either side of the bicycle wheel to frictionally engage the rim of the bicycle wheel.
The operation of conventional hydraulic systems incorporating a hand actuated mechanism, as described above, is somewhat restricted by limiting factors that impede the efficient performance of the brake system. One such limiting factor exists in the amount of displacement of the actuating handle of the mechanism, which is limited to the gripping range of the bicycle rider's hand. Another limiting factor exists in the need for a reasonable running clearance that must be maintained between the friction pads and the rim of the bicycle. Due to this necessary running clearance there is a minimum distance the friction pads must travel from the rest state to the actuated or braking state. These factors contribute toward limiting the magnitude of a constant mechanical advantage possible with the above described system. Conventional systems have also been unsatisfactory since in wet weather conditions the pad-to-rim friction coefficient drops to about half, consequently resulting in the application of increased effort to enforce braking conditions
Additionally, a consistent relationship between the hand lever displacement and the braking action which is provided by brake pads is essential for predictable operation. For example, since brake pads have a tendency to wear, and thus become thinner, additional displacement of the piston in the slave cylinder is required for the pads to effectively engage the wheel rim. Thus, the degree of manual displacement of the hand lever required to cause brake pad-to-rim contact varies as the brake pads wear. It is desireable to have a self-adjusting system which would avoid the frequent maintenance required to adjust brake pads for wear.
Although hydraulic brake systems are commonplace on automobiles, such systems are known to be characterized by disadvantages, some of which are enumerated below. Conventional hydraulic brake systems for automobiles typically have a brake fluid reservoir and a master cylinder with a master piston, in fluid communication with slave cylinders. Such systems are known to incorporate the use of a check valve member constructed and arranged to control fluid flow from the master cylinder to the slave cylinders. Some such conventional hydraulic brake systems employ a ball check valve member that is spring biased against the valve seat to limit the flow of fluid. An automobile master cylinder typically employs a very small hole, in the master cylinder for providing fluid communication with the fluid reservoir. Typically, the master cylinder is horizontally oriented proximate to and below the fluid reservoir, so that brake fluid flows by gravity, from the reservoir, via the hole, to the master cylinder. The hole is small, for example 0.04 inch in diameter to prevent the rubber cup or seal on the piston of the master cylinder from extruding through the hole during operation. Thus the rate of fluid flow through the small hole is slow and insufficient to rapidly replenish fluid to account for adjustment and bleeding. To overcome this disadvantage, some automotive master cylinders employ auxiliary openings between the fluid reservoir and the master cylinder, to provide additional fluid flow paths to replenish fluid in the brake system. However, the auxiliary openings also cause increased manufacturing costs and maintenance requirements.
In such master cylinders, another limiting factor resulting from the horizontal orientation of the master cylinder for the rate of fluid replenishment is the tolerances that must be held for the cup to prevent extrusion under pressure. The cup must collapse during the return stroke and fluid must pass by the close tolerance parts. Additionally, when the friction pads need to be replaced, and the caliper or slave pistons are manually retracted, the fluid must pass through the small diameter hole and back into the reservoir which is facilitated by a C-Clamp.
Another limiting factor in the typical master cylinder design is the relationship between the bore length and the stroke of the piston, wherein the minimum bore length is increased to accommodate larger springs because the required spring rate is considerable to collapse the cup and pull fluid from the reservoir during fluid replenishment.
For example, U.S. Pat. Nos. 2,385,625 to Hopmans; 2,503,488 to Huffman; 2,571,963 to Stelzer; 2,746,575 to Kinchin; and 2,961,831 to Brueder show various schemes that incorporate an auxiliary valve for automatic adjustment of the fluid content in hydraulic transmission systems to compensate for wear and movement in the brake system.
Thus, it is desirable to provide a hydraulic system incorporating a valve member that eliminates the use of auxiliary openings, yet still provides sufficient flow between the master cylinder and the reservoir. Likewise, it is desirable also to orient the valve member such that when the brake pads are manually pushed away from the rim of the wheel, for example, when changing the brake pads or wheel, the fluid returning to the master cylinder from the slave cylinders encounters minimal interference from the valve member. To facilitate maintenance, it is also desireable for the master cylinder assembly to be easily removable from the bicycle by disassembling the brake lines so that the brake system can be repaired without bringing the entire bicycle to the repair shop.
Thus, a need exists for an efficient hydraulic braking system for bicycles with a combination of improvements interacting to substantially enhance performance and reduce maintenance of the braking system.